Reflected signal absorption in interconnect

ABSTRACT

Embodiments of the present disclosure are directed toward techniques and configurations for electrical signal absorption in an interconnect stub. In one instance, a printed circuit board (PCB) assembly may comprise a substrate and an interconnect (such as a via) formed in the substrate to route an electrical signal within the PCB. The interconnect may include a stub formed on the interconnect. At least a portion of the stub may be covered with an absorbing material to at least partially absorb a portion of the electric signal that is reflected by the stub. The absorbing material may be selected such that its dielectric loss tangent is greater than one, for a frequency range of a frequency of the reflected portion of the electric signal. A dielectric constant of the absorbing material may be inversely proportionate to the frequency of the reflected electric signal. Other embodiments may be described and/or claimed.

This application is a divisional application of U.S. patent applicationSer. No. 14/303,396, entitled “REFLECTED SIGNAL ABSORPTION ININTERCONNECT”, filed Jun. 12, 2014, and claims priority to the Ser. No.14/303,396 application. The Specification of Ser. No. 14/303,396 ishereby fully incorporated by reference.

FIELD

Embodiments of the present disclosure generally relate to the field ofprinted circuit board design, and more particularly, to techniques andconfigurations for reducing reflected noise signals in interconnectsused in the printed circuit boards.

BACKGROUND

Electric signals within multilayered printed circuit boards (PCB),silicon dies, or package substrates are routed through interconnects,such as vias, connectors, transmission lines, and the like. Someinterconnects may have stubs formed on the interconnects due to designrequirements or manufacturing limitations. For example, a via mayprovide a vertical electrical connection between two layers of the PCBs.A portion of the via that is not used for signal routing may form astub. When transitioning through the interconnect, an electric signalmay be split into two portions: one portion (desired transmissionsignals) may travel through the interconnect toward the receiving point(e.g., via the conductive line coupled with the interconnect), and theother portion may travel into the stub, creating reflected noisesignals. The reflected noise signals may distort desired signals passingthrough the connector and decrease the usable bandwidth of theinterconnect. Existing techniques aimed at reducing reflected noisesignals, such as back-drilling, reducing signal routing length, orlowering the speed of signal transmission, may be costly and oftenineffective, for at least certain types of interconnects.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. To facilitatethis description, like reference numerals designate like structuralelements. Embodiments are illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings.

FIG. 1 illustrates a cross-section side view of an example printedcircuit board (PCB) assembly 100, in accordance with some embodiments.

FIG. 2 schematically illustrates a transmission line placed within asubstrate, with a transmission line stub to be covered with anabsorption material, in accordance with some embodiments.

FIG. 3 schematically illustrates an edge connector placed on asubstrate, with an edge connector stub to be covered with an absorptionmaterial, in accordance with some embodiments.

FIGS. 4-6 schematically illustrate an example PCB assembly subsequent tovarious fabrication operations adapted to apply an absorption materialto the PCB interconnect stubs, in accordance with some embodiments.

FIG. 7 is a process flow diagram for providing an absorption material tointerconnect stubs of interconnects in an apparatus, such as a PCBassembly, in accordance with some embodiments.

FIG. 8 schematically illustrates a computing device including a PCBassembly in accordance with some embodiments.

DETAILED DESCRIPTION

Embodiments of the present disclosure describe techniques andconfigurations for electrical signal reflection/absorption that mayinclude interconnects such as vias having stubs at least partiallycovered with an absorption material to at least partially absorb areflected portion of a signal traveling through the interconnect. In thefollowing description, various aspects of the illustrativeimplementations will be described using terms commonly employed by thoseskilled in the art to convey the substance of their work to othersskilled in the art. However, it will be apparent to those skilled in theart that embodiments of the present disclosure may be practiced withonly some of the described aspects. For purposes of explanation,specific numbers, materials, and configurations are set forth in orderto provide a thorough understanding of the illustrative implementations.However, it will be apparent to one skilled in the art that embodimentsof the present disclosure may be practiced without the specific details.In other instances, well-known features are omitted or simplified inorder not to obscure the illustrative implementations.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the subject matter of the presentdisclosure may be practiced. It is to be understood that otherembodiments may be utilized and structural or logical changes may bemade without departing from the scope of the present disclosure.Therefore, the following detailed description is not to be taken in alimiting sense, and the scope of embodiments is defined by the appendedclaims and their equivalents.

For the purposes of the present disclosure, the phrase “A and/or B”means (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B, and C).

The description may use perspective-based descriptions such astop/bottom, in/out, over/under, and the like. Such descriptions aremerely used to facilitate the discussion and are not intended torestrict the application of embodiments described herein to anyparticular orientation.

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous.

The term “coupled with,” along with its derivatives, may be used herein.“Coupled” may mean one or more of the following. “Coupled” may mean thattwo or more elements are in direct physical or electrical contact.However, “coupled” may also mean that two or more elements indirectlycontact each other, but yet still cooperate or interact with each other,and may mean that one or more other elements are coupled or connectedbetween the elements that are said to be coupled with each other. Theterm “directly coupled” may mean that two or more elements are in directcontact.

In various embodiments, the phrase “a first layer formed, deposited, orotherwise disposed on a second layer” may mean that the first layer isformed, deposited, or disposed over the second layer, and at least apart of the first layer may be in direct contact (e.g., direct physicaland/or electrical contact) or indirect contact (e.g., having one or moreother layers between the first layer and the second layer) with at leasta part of the second layer.

As used herein, the term “module” may refer to, be part of, or includean Application Specific Integrated Circuit (ASIC), an electroniccircuit, a processor (shared, dedicated, or group), and/or memory(shared, dedicated, or group) that execute one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality.

The described techniques provide for at least partial absorption of thereflected portions of the electric signals routed through aninterconnect. The reflected signals may be absorbed, at least partially,by an absorption material applied to at least a portion of the stub, forexample, a bottom portion of the stub. To provide the desired absorptionlevel, the absorption material may be selected to satisfy certainconditions. For example, a desired absorption may be achieved when theabsorption material has a dielectric loss tangent that is greater thanone for a frequency range of a frequency of the reflected signal and adielectric constant that is inversely proportional to the frequency ofthe reflected signal. Types of interconnects with stubs that may becovered with absorption material may include vias, transmission lines,edge (e.g., gold finger) connectors, and the like.

The embodiments of the present disclosure will be described in referenceto FIGS. 1-3. The embodiments may include an apparatus comprising adielectric layer and an interconnect (e.g., formed in the dielectriclayer) to route an electrical signal through the dielectric layer, wherethe interconnect includes a stub formed on the interconnect, and atleast a portion of the stub is covered with an absorption material to atleast partially absorb a portion of the electric signal that isreflected by the stub. In some embodiments, the apparatus may comprise aPCB assembly, a die, a package substrate, or a printed circuit board.More generally, the apparatus may comprise any structure pertaining to aflip chip configuration or direct chip attach (DCA) configuration.

FIG. 1 illustrates a cross-section side view of an example printedcircuit board (PCB) assembly 100, in accordance with some embodiments.The PCB assembly 100 may comprise a substrate 102. The substrate 102 maybe an organic substrate made of dielectric material including, forexample, build-up layers (not shown) configured to route electricalsignals through the PCB assembly 100. The PCB assembly may include oneor more interconnects (such as interconnect 104) configured to routeelectrical signals 106 such as, for example, input/output (I/O) signalsand/or power or ground signals associated with the operation of the PCBassembly 100. In some embodiments, the interconnect 104 may comprise avia filled with a conductive material, such as copper, to provide forelectrical conductivity for the incoming signal 106.

In some embodiments, the incoming signal 106 may be routed via anelectrically conductive line (e.g., transmission line 110) into theinterconnect 104, to a receiving point (not shown) via anotherelectrically conductive line 112, as shown. Accordingly, the incomingsignal may be split into two portions. One portion, a desiredtransmission signal 118, may travel to the receiving point via theconductive line 112, while another portion may continue travelingthrough a stub portion 122 of the interconnect 104, forming a reflectednoise signal 120. The reflected noise signal 120 may comprise surfacewaves and/or evanescent waves, and may include some propagating waves.

The PCB assembly 100 may further comprise a layer of an absorptionmaterial 130 that may be disposed about at least a portion of the stub122. For example, as shown in FIG. 1, the absorption material 130 maycover at least a bottom of the stub 122 forming an end of theinterconnect 104. The absorption material 130 covering a portion of thestub 122 may at least partially absorb the reflected noise signal 120 onthe stub 122, thus reducing inter-symbol interference (ISI) and harmfulcoupling, and correcting timing jitter that may be induced by thereflected noise signal 120. The reduction of the reflected noise signal120 using the absorption material 130 to cover the stub 122 may beparticularly effective in the high speed signaling.

Besides via stubs such as the stub 122, the absorption material 130 maybe used to mitigate the stub effects for other types of interconnectsthat may be used in high speed signaling and interconnects. Otherinterconnect types may include, for example, transmission lines or edgeconnectors (“gold finger” connectors), which are described in referenceto FIGS. 2 and 3, respectively.

FIG. 2 schematically illustrates a transmission line placed within asubstrate, with a transmission line stub to be covered with anabsorption material, in accordance with some embodiments. As shown, atransmission line 202 may be disposed in a substrate (e.g., PCBsubstrate) 204. The transmission line 202 may include a stub 206extending from the transmission line 202. The absorption material may beapplied to cover or embed the stub 206 as indicated by arrow 210. Forinternal routing transmission line 202 (e.g., stripline), a via may bedrilled to an upper layer of the PCB substrate 204 to connect with thestub 206 (not shown). For external routing (e.g., micro-stripline), theabsorption material may be disposed on top of the PCB substrate 204, topartially cover the upper layer and the connection with stub 206.

FIG. 3 schematically illustrates an edge connector placed on asubstrate, with an edge connector stub to be covered with an absorptionmaterial, in accordance with some embodiments. As shown, an edgeconnector (e.g., “gold finger” connector) 300 may include a pair of“fingers” 302 and 304 and may be disposed about the edge of the PCBsubstrate 306. The “fingers” 302 and 304 may include one or more stubs,such as stubs 308 and 310, respectively. The absorption material may beapplied to at least portions of the stubs 308 and 310 as indicated byarrows 320. For example, the absorption material may be added to thebottom of a connector in which the edge connector 300 may be plugged.

In some embodiments, the absorption material 130 may be selected so asto cause the reflected noise signal 120 comprising, e.g.,electromagnetic waves entering the absorption material 130 to attenuatequickly and dissipate as heat, thus reducing or eliminating thereflected noise signal 120. The wave propagation factor forelectromagnetic wave of the reflected noise signal 120 may be derived asfollows.

The electromagnetic wave number in vacuum (free space) may be defined as

$k_{0} = \frac{2\pi}{\lambda_{0}}$

where k₀ and λ_(O) are the electromagnetic wave number and wavelength invacuum. The electromagnetic wave number in media k (e.g., absorptionmaterial with relative permittivity {tilde over (∈)}_(r) and relativepermeability {tilde over (μ)}_(r)) may be written as

k=k ₀√{square root over ({tilde over (μ)}_(r){tilde over (∈)}_(r))}

Since {tilde over (∈)}_(r)=∈_(r) (1+j tan δ), where tan δ is losstangent of the absorption material, δ is the angle of loss tangent,∈_(r) is relative dielectric constant of the absorption material, andnon-magnetic material permeability {tilde over (μ)}_(r)=1, theelectromagnetic wave number k may be defined as

k=k ₀√{square root over (∈_(r)(1+j tan δ))},

where j is the imaginary unit.The wave propagation factor may be derived from a Maxwell equationfollowing the following sequence of expressions:

${\exp \left( {j\; {kd}} \right)} = {\exp \left( {j\; {dk}_{0}\sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)}} \right)}$or${\exp \left( {j\; {kd}} \right)} = {\exp \left( {j\; d\frac{2\pi}{\lambda_{0}}\sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)}} \right)}$

where d is the distance of wave propagation inside the absorptionmaterial and λ₀ is wavelength of free space. The above expression may bewritten as follows:

${\exp \left( {j\; {kd}} \right)} = {\exp \left( {j\; d{\frac{2\pi}{\lambda_{0}}\left\lbrack {{{real}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)} + {j \cdot {{imag}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}}} \right\rbrack}} \right)}$  or${\exp \left( {j\; {kd}} \right)} = {\exp \left( {d{\frac{2\pi}{\lambda_{0}}\left\lbrack {{j\mspace{11mu} {{real}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}} - {{imag}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}} \right\rbrack}} \right)}$

The final expression may be written as follows:

${\exp \left( {j\; {kd}} \right)} = {{\exp \left( {j\; d\frac{2\pi}{\lambda_{0}}{{real}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}} \right)}{\exp \left( {{- d}\frac{2\pi}{\lambda_{0}}{{imag}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}} \right)}}$

with loss factor being

${\exp \left( {{- d}\frac{2\pi}{\lambda_{0}}{{imag}\left( \sqrt{ɛ_{r}\left( {1 + {j\mspace{11mu} \tan \; \delta}} \right)} \right)}} \right)}.$

Based on electromagnetic wave theory and the above expressions, thereflected waves may be ideally (fully) absorbed, if the absorptionmaterial satisfies the following conditions:

-   -   the loss tangent, tan δ, may be above one (>1) for a frequency        range of a frequency of the reflected noise signal and, in ideal        conditions, may remain constant across the frequency range;    -   the dielectric constant, ∈_(r), may be inversely proportional to        frequency, so that the loss factor may remain constant for the        frequency range of the frequency of the reflected noise signal.

The above requirements are formulated for ideal absorption (e.g.,elimination) of reflected noise signal by an absorption material.Different types of absorption materials with properties approximating orsatisfying the above conditions with desired threshold margins may beused to at least partially absorb reflected noise signals in theinterconnect stubs. For example, absorption materials may be used thatare produced by Cuming Microwave Corporation, MAST, Western Rubber andSupply, Inc., and the like. For example, Cuming Microwave Corporation'sC-RAM MT-30 absorption material may be used for the purposes of at leastpartial absorption of a reflected noise signal.

FIGS. 4-6 schematically illustrate an example PCB assembly subsequent tovarious fabrication operations adapted to apply an absorption materialto the PCB interconnect stubs, in accordance with some embodiments. Forillustration purposes, the example PCB assembly may comprise a centralprocessing unit (CPU) socket that provides mechanical and electricalconnections between a processor and a PCB in a computing apparatus.

Referring to FIG. 4, a back view of an example CPU socket 400 is shown.The CPU socket 400 may be disposed on a PCB substrate 402, a portion ofwhich is shown in FIG. 4, with removed cover plate. The CPU socket 400may include an array of vias such as dense via array 404. In FIGS. 4-6,the PCB assembly 400 may include a substrate 402 made of a dielectric(e.g., organic) material, similar to the substrate 102 discussed above.The PCB assembly may also include other components, such as conductivelines 406 or decoupling capacitors 408.

Referring to FIG. 5, the CPU socket 400 is depicted subsequent to addinga piece of absorption material 506 to cover the via array 404 under theCPU socket 400. The absorption material may be disposed on the via array404 by means of gluing or fastening, for example.

In another example, the absorption material may be retained on the viaarray 404 by using pressure provided by a socket retention mechanism.Referring to FIG. 6, retention elements 602 (e.g., screws, bolts, orother equivalent components) may be provided through the substrate 402,to connect the socket retention mechanism (not shown) with a cover plate604. Referring to FIG. 6, the CPU socket 400 is depicted subsequent toplacing the cover plate 604 onto the CPU socket 400, with the coverplate 604 kept in place by the retention elements 602.

The cover plate 602 connected through the substrate 402 with the socketretention mechanism may apply pressure to the absorption materialcovered by the cover plate 604, retaining the material in place tosubstantially cover the via array 404. The cover plate may compress theabsorption material, which may include a foam-like material, reducingthe cell size of the absorption material.

FIG. 7 is a process flow diagram for providing an absorption material tostubs of interconnects in an apparatus, such as a PCB assembly, inaccordance with some embodiments. The process 700 may comport withactions described in connection with FIGS. 1-6 in some embodiments.

At block 702, one or more interconnects may be formed in a printedcircuit board (PCB) assembly to route electrical signals within the PCB.In some embodiments, the interconnects may comprise vias or other typesof interconnects, described in reference to FIGS. 1-3. In someembodiments, the interconnects may comprise a via array such as viaarray 404 described in reference to FIGS. 4-6. Forming interconnects mayinclude disposing electrically conductive material inside theinterconnects (e.g., vias) to enable routing of the electrical signals.At least some of the interconnects may include stubs formed on theinterconnects as described in reference to FIGS. 1-3.

At block 704, an absorption material may be applied to at least portionsof the interconnect stubs, to absorb (at least partially) portions ofthe electric signals reflected by the stubs, e.g., the reflected noisesignals described in reference to FIG. 1. The absorption material may beapplied in a number of different ways described in reference to FIGS.2-6. For example, the interconnects may be dense vias having stub endsthat are exposed on a surface of the PCB. Applying an absorptionmaterial may include covering stub ends with the absorption material asdescribed in reference to FIGS. 4-6.

In some embodiments, prior to applying the absorption material to theinterconnect stubs, the absorbing material may be selected according tothe criteria described above. For example, the absorbing material may beselected such that a dielectric loss tangent of the absorbing materialmay be greater than one, for a frequency range of a frequency of thereflected portions of the electric signals. The absorbing material maybe further selected such that a relative dielectric constant of theabsorbing material may be inversely proportionate to the frequency ofthe reflected portions of the electric signals.

At block 706, the absorbing material may be retained in place byfastening, gluing, applying pressure, or other methods described above.

FIG. 8 schematically illustrates a computing device 800 including atleast a PCB assembly in accordance with some embodiments. The computingdevice 800 may house a board such as motherboard 802. The motherboard802 may be implemented as the PCB assembly 100 described in reference toFIG. 1. The motherboard 802 may include a number of components,including but not limited to a processor 804 and at least onecommunication chip 806. The processor 804 may be physically andelectrically coupled to the motherboard 802. In some implementations,the at least one communication chip 806 may also be physically andelectrically coupled to the motherboard 802. In further implementations,the communication chip 806 may be part of the processor 804.

Depending on its applications, computing device 800 may include othercomponents that may or may not be physically and electrically coupled tothe motherboard 802. These other components may include, but are notlimited to, volatile memory (e.g., dynamic random-access memory (DRAM))820, non-volatile memory (e.g., read-only memory (ROM)) 824, flashmemory 822, a graphics processor 830, a digital signal processor or acrypto processor (not shown), a chipset 826, an antenna 828, a display(e.g., touchscreen display) 832, a touchscreen controller 846, a battery836, a power amplifier 841, a global positioning system (GPS) device840, a compass 842, a speaker 850, a camera 852, a mass storage device(such as hard disk drive, compact disk (CD), or digital versatile disk(DVD)), an audio codec, a video codec, a Geiger counter, anaccelerometer, a gyroscope (not shown), and so forth.

The communication chip 806 may enable wireless communications for thetransfer of data to and from the computing device 800. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 806 may implement anyof a number of wireless standards or protocols, including but notlimited to Institute for Electrical and Electronic Engineers (IEEE)standards including Wi-Fi (IEEE 802.11 family), IEEE 802.16 standards(e.g., IEEE 802.16-2005 Amendment), Long-Term Evolution (LTE) projectalong with any amendments, updates, and/or revisions (e.g., advanced LTEproject, ultra mobile broadband (UMB) project (also referred to as“3GPP2”), etc.). IEEE 802.16 compatible broadband wireless access (BWA)networks are generally referred to as WiMAX networks, an acronym thatstands for Worldwide Interoperability for Microwave Access, which is acertification mark for products that pass conformity andinteroperability tests for the IEEE 802.16 standards. The communicationchip 806 may operate in accordance with a Global System for MobileCommunication (GSM), General Packet Radio Service (GPRS), UniversalMobile Telecommunications System (UMTS), High Speed Packet Access(HSPA), Evolved HSPA (E-HSPA), or LTE network. The communication chip806 may operate in accordance with Enhanced Data for GSM Evolution(EDGE), GSM EDGE Radio Access Network (GERAN), Universal TerrestrialRadio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). Thecommunication chip 806 may operate in accordance with Code DivisionMultiple Access (CDMA), Time Division Multiple Access (TDMA), DigitalEnhanced Cordless Telecommunications (DECT), Evolution-Data Optimized(EV-DO), derivatives thereof, as well as any other wireless protocolsthat are designated as 3G, 4G, 5G, and beyond. The communication chip806 may operate in accordance with other wireless protocols in otherembodiments.

The computing device 800 may include a plurality of communication chips806. For instance, a first communication chip 806 may be dedicated toshorter range wireless communications such as Wi-Fi and Bluetooth, and asecond communication chip 806 may be dedicated to longer range wirelesscommunications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, EV-DO, andothers.

The processor 804 of the computing device 800 may include a die or apackage substrate as described herein. For example, a package substrate(e.g., substrate 402 of FIG. 2) having the die mounted thereon may becoupled with a circuit board such as, for example, motherboard 802,using package-level interconnects such as, for example, ball-grid array(BGA) or land-grid array (LGA) structures. The term “processor” mayrefer to any device or portion of a device that processes electronicdata from registers and/or memory to transform that electronic data intoother electronic data that may be stored in registers and/or memory.

The communication chip 806 may also include a die or a package substrateas described herein. In further implementations, another component(e.g., memory device or other integrated circuit device) housed withinthe computing device 800 may contain a die or package substrate asdescribed herein.

In various implementations, the computing device 800 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 800 may be any other electronic device that processes data.

According to various embodiments, the present disclosure describes anumber of examples. Example 1 is a printed circuit board (PCB) assemblyfor absorbing reflected electric signal, comprising: a substrate and atleast one interconnect formed in the substrate to route an electricalsignal within the PCB, wherein the interconnect includes a stub formedon the interconnect, wherein at least a portion of the stub is coveredwith an absorbing material to at least partially absorb a portion of theelectric signal that is reflected by the stub.

Example 2 may include the subject matter of Example 1, and furtherspecifies that the interconnect comprises a via that extends through thesubstrate, wherein the stub is formed by at least a portion of the via,a bottom of the stub that forms an end of the via.

Example 3 may include the subject matter of Example 2, and furtherspecifies that the portion of the stub covered with the absorbingmaterial includes at least the bottom the stub.

Example 4 may include the subject matter of Example 1, and furtherspecifies that the interconnect comprises a gold finger connector.

Example 5 may include the subject matter of Example 1, and furtherspecifies that the interconnect comprises a transmission line thatextends through the substrate.

Example 6 may include the subject matter of Example 1, and furtherspecifies that the electrical signal comprises a transmission signaltransmitted with a speed above a threshold.

Example 7 may include the subject matter of Example 1, and furtherspecifies that a dielectric loss tangent of the absorbing material isgreater than one, for a frequency range of a frequency of the reflectedportion of the electric signal that is to be at least partiallyabsorbed.

Example 8 may include the subject matter of Example 7, and furtherspecifies that a relative dielectric constant of the absorbing materialis inversely proportionate to the frequency of the reflected portion ofthe electric signal that is to be at least partially absorbed.

Example 9 may include the subject matter of Example 8, and furtherspecifies that the dielectric loss tangent of the absorbing material issubstantially constant for the frequency range of the frequency of thereflected portion of the electric signal that is to be at leastpartially absorbed.

Example 10 may include the subject matter of Example 1, and furtherspecifies that the absorbing material comprises Cuming MicrowaveCorporation® C-RAM MT-30.

Example 11 may include the subject matter of Examples 1-10, and furtherspecifies that the at least one interconnect comprises a centralprocessing unit (CPU) socket.

Example 12 may include an apparatus for absorbing reflected electricsignal, comprising: at least one dielectric layer; and an interconnectformed in the at least one dielectric layer to route an electricalsignal through the dielectric layer, wherein the interconnect includes astub formed on the interconnect, wherein at least a portion of the stubis covered with an absorbing material to at least partially absorb aportion of the electric signal that is reflected by the stub.

Example 13 may include the subject matter of Example 12, and furtherspecifies that the apparatus comprises a die that includes the at leastone dielectric layer and the interconnect.

Example 14 may include the subject matter of Example 12, and furtherspecifies that the apparatus comprises a package substrate that includesthe at least one dielectric layer and the interconnect.

Example 15 may include the subject matter of Example 12, and furtherspecifies that the apparatus comprises a printed circuit board thatincludes the at least one dielectric layer and the interconnect.

Example 16 may include the subject matter of Example 12, and furtherspecifies that the interconnect comprises one of: a via that extendsthrough the dielectric layer and has an electrically conductive materialdisposed within the via to provide electrical connectivity for routingthe electrical signal, or a transmission line that extends through thedielectric layer.

Example 17 may include the subject matter of Example 12, and furtherspecifies that the absorbing material has a dielectric loss tangent thatis greater than one, for a frequency range of a frequency of thereflected portion of the electric signal that is to be at leastpartially absorbed.

Example 18 may include the subject matter of Examples 12-17, and furtherspecifies that the absorbing material has a relative dielectric constantthat is inversely proportionate to the frequency of the reflectedportion of the electric signal that is to be at least partiallyabsorbed.

Example 19 may include a method for absorbing reflected electric signal,comprising: forming one or more interconnects in a printed circuit board(PCB) assembly to route electrical signals within the PCB, at least someof the interconnects having stubs formed on the interconnects; andapplying an absorbing material to at least portions of the stubs, to atleast partially absorb portions of the electric signals reflected by thestubs.

Example 20 may include the subject matter of Example 19, and furtherspecifies that the one or more interconnects comprise vias, whereinforming one or more interconnects includes disposing electricallyconductive material inside the vias to enable routing of the electricalsignals.

Example 21 may include the subject matter of Example 20, and furtherspecifies that the vias comprise dense vias having stub ends that areexposed on a surface of the PCB, wherein applying the absorbing materialincludes covering the stub ends with the absorbing material.

Example 22 may include the subject matter of Example 21, and furtherspecifies that the vias comprise a via array.

Example 23 may include the subject matter of Example 22, and furtherspecifies that the PCB comprises a central processing unit (CPU) socket.

Example 24 may include the subject matter of Example 23, and furtherspecifies that the method further includes covering the CPU socket witha cover plate to retain the absorbing material in place to cover the viaarray.

Example 25 may include the subject matter of Examples 19 to 24, andfurther specifies that the method further includes selecting theabsorbing material such that a dielectric loss tangent of the absorbingmaterial is greater than one, for a frequency range of a frequency ofthe reflected portions of the electric signals, and a relativedielectric constant of the absorbing material is inversely proportionateto the frequency of the reflected portions of the electric signals.

Various embodiments may include any suitable combination of theabove-described embodiments including alternative (or) embodiments ofembodiments that are described in conjunctive form (and) above (e.g.,the “and” may be “and/or”). Furthermore, some embodiments may includeone or more articles of manufacture (e.g., non-transitorycomputer-readable media) having instructions, stored thereon, that whenexecuted result in actions of any of the above-described embodiments.Moreover, some embodiments may include apparatuses or systems having anysuitable means for carrying out the various operations of theabove-described embodiments.

The above description of illustrated implementations, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments of the present disclosure to the precise formsdisclosed. While specific implementations and examples are describedherein for illustrative purposes, various equivalent modifications arepossible within the scope of the present disclosure, as those skilled inthe relevant art will recognize.

These modifications may be made to embodiments of the present disclosurein light of the above detailed description. The terms used in thefollowing claims should not be construed to limit various embodiments ofthe present disclosure to the specific implementations disclosed in thespecification and the claims. Rather, the scope is to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

What is claimed is:
 1. A printed circuit board (PCB) assemblycomprising: a substrate; and at least one interconnect formed in thesubstrate to form an electrically conductive line to route an electricalsignal within the PCB, wherein the interconnect includes a stub formedon the interconnect, wherein the stub forms an electric path thatextends away from the electrically conductive line, wherein the electricsignal includes a desired transmission signal portion to travel via theelectrically conductive line and a stub signal portion to travel throughthe stub, to form a reflected noise signal in response to a reflectionby an end of the stub, wherein at least a portion of the end of the stubis covered with an absorbing material to at least partially absorb theportion of the electric signal that is reflected by the end of the stub,wherein the absorbing material has a dielectric loss tangent that isgreater than a determined value, and remains substantially constant, fora frequency range of a frequency of the reflected portion of theelectric signal that is to be at least partially absorbed.
 2. The PCBassembly of claim 1, wherein the interconnect comprises a via thatextends through the substrate, wherein the stub is formed by at least aportion of the via, wherein a bottom of the stub forms an end of thevia.
 3. The PCB assembly of claim 2, wherein the portion of the stubcovered with the absorbing material includes at least the bottom thestub.
 4. The PCB assembly of claim 1, wherein the interconnect comprisesa gold finger connector.
 5. The PCB assembly of claim 1, wherein theinterconnect comprises a transmission line that extends through thesubstrate.
 6. The PCB assembly of claim 1, wherein the electrical signalcomprises a transmission signal transmitted with a speed above athreshold.
 7. The PCB assembly of claim 1, wherein the determined valueof the dielectric loss tangent of the absorbing material is greater than1, for a frequency range of a frequency of the reflected portion of theelectric signal that is to be at least partially absorbed.
 8. The PCBassembly of claim 7, wherein a relative dielectric constant of theabsorbing material is inversely proportionate to the frequency of thereflected portion of the electric signal that is to be at leastpartially absorbed.
 9. The PCB assembly of claim 8, wherein thedielectric loss tangent of the absorbing material is substantiallyconstant for the frequency range of the frequency of the reflectedportion of the electric signal that is to be at least partiallyabsorbed.
 10. The PCB assembly of claim 1, wherein the absorbingmaterial comprises Cuming Microwave Corporation® C-RAM MT-30.
 11. ThePCB assembly of claim 1, wherein the at least one interconnect comprisesa central processing unit (CPU) socket.
 12. A method, comprising:forming an interconnect in a printed circuit board (PCB) assembly toroute electrical signals within the PCB via an electrically conductiveline, the interconnect having a stubs formed on the interconnect,wherein a stub forms an electric path that extends away from theelectrically conductive line, wherein the electric signal includes adesired transmission signal portion to travel via the electricallyconductive line and a stub signal portion to travel through the stub, toform a reflected noise signal in response to a reflection by an end ofthe stub; and applying an absorbing material to at least a portion ofthe stubs, to at least partially absorb portions of the electric signalsreflected by the end of the stub, wherein the absorbing material has adielectric loss tangent that is greater than a determined value, andremains substantially constant, for a frequency range of a frequency ofthe reflected portion of the electric signal that is to be at leastpartially absorbed.
 13. The method of claim 12, wherein the interconnectcomprises a via, wherein forming the interconnect includes disposingelectrically conductive material inside the via to enable routing of theelectrical signals.
 14. The method of claim 13, wherein the viacomprises a dense via having the stub end that is exposed on a surfaceof the PCB, wherein applying the absorbing material includes coveringthe stub end with the absorbing material.
 15. The method of claim 14,wherein the via comprises a via array.
 16. The method of claim 15,wherein the PCB comprises a central processing unit (CPU) socket. 17.The method of claim 16, further comprising: covering the CPU socket witha cover plate to retain the absorbing material in place to cover the viaarray.
 18. The method of claim 12, further comprising: selecting theabsorbing material such that a dielectric loss tangent of the absorbingmaterial is greater than the determined value, for a frequency range ofa frequency of the reflected portions of the electric signals, and arelative dielectric constant of the absorbing material is inverselyproportionate to the frequency of the reflected portions of the electricsignals.